Why shouldn't tests be run on a production server?
From semantic-mediawiki.org
Fragment of a discussion from Help talk:Installation
It is an established practice that you run tests (unit or integration) not on a production cluster unless you have a specific task you'd like to verify.
Aside from the mentioned best practice, tests try not to leak any setup information (meaning any data required for the tests) into a test/production database by cloning all tables into a different namespace (prefix) but it may happen (happened in the past as we rely on MW's `CloneDatabase` but I haven't seen it happen as of late).
